This invention relates generally to absorbent structures used in disposable articles such as diapers, children's training pants, feminine care articles, incontinence articles, bandages, surgical gowns, absorbent wipes and the like, and more particularly to such absorbent structures containing a superabsorbent material having enhanced liquid handling characteristics such as an enhanced combination of retention capacity, free swell gel bed permeability and/or absorbency under load value.
Conventional disposable articles typically include an absorbent structure, also sometimes referred to as an absorbent core or absorbent composite, formed by air-forming, air-laying or other known forming technique. For example, the manufacture of such an absorbent structure may begin by fiberizing a fibrous sheet of hydrophilic material in a fiberizer or other shredding or comminuting device to form discrete fibers. In addition, particles or fibers of superabsorbent material, which are water insoluble, water swellable and capable of absorbing at least about ten times their weight in 0.9 weight percent sodium chloride solution in distilled water (saline solution), are mixed with the discrete fibers. The hydrophilic fibers and superabsorbent material are then entrained in an air stream and directed to a foraminous forming surface upon which the fibers and superabsorbent material are deposited and accumulated to form the absorbent structure.
There is a continuing effort by absorbent structure manufacturers to improve the liquid intake performance of absorbent structures to thereby reduce the tendency of such a structure to leak as it becomes increasingly saturated during use, particularly where the structure is subjected to repeated liquid insults before being discarded. For example, one means of reducing the leakage of absorbent structures has been the extensive use of superabsorbent materials. In addition to increasing the amount of superabsorbent mass, recent efforts in commercial absorbent structure design have generally focused on using a higher concentration of superabsorbent material and less fiber to make the absorbent structure thinner and denser.
However, notwithstanding the increase in total absorbent capacity obtained by increasing the concentration of superabsorbent material, such absorbent structures may still leak during use. The leakage may be in part the result of the structure having an insufficient intake rate, e.g., the rate at which a liquid insult can be taken into and entrained within the structure for subsequent absorption by the superabsorbent material. More particularly, the intake rate of such absorbent structures may decrease upon repeated insults thereof due to the tendency of the superabsorbent material within the structure to swell as it absorbs and thus restrict or otherwise block the open channels between superabsorbent particles, or between the particles and the hydrophilic fibers within the absorbent structure. This phenomenon is often referred to as a form of gel-blocking and may occur as a result of the superabsorbent material lacking sufficient gel integrity or reaching such a high degree of swelling that it tends to be easily deformable under an external pressure, such as those loads applied by a wearer during movement or upon sitting down.
The in-use performance of an absorbent structure may therefore rely upon 1) the ability to create open channels and void volume within the absorbent structure and 2) the ability to maintain the openness of and accessibility to such channels and void volume upon saturation of the absorbent structure. The ability to create the open channels may be a function of the ability of the superabsorbent material to absorb liquid while the material is under pressure as well as the ability to retain liquid and not deform while under pressure. Liquid handling characteristics commonly associated with such functions include the retention capacity (CRC) and the absorbency under load (AUL) value of the superabsorbent material. The ability to maintain openness of and accessibility to the channels and void volume may be in large part a function of the gel bed permeability (GBP) of the superabsorbent material. A higher GBP indicates a higher ability to maintain open channels within the absorbent structure after the superabsorbent material is saturated and fully swollen.
To date, research efforts directed toward improving the liquid handling characteristics of absorbent structures have generally been focused on enhancing the gel bed permeability of the superabsorbent material within absorbent structures. However, such an approach has come at a cost in the form of reduced or at least a lack of enhanced retention capacity.
There is a need, therefore, for absorbent structures incorporating superabsorbent materials having a high gel bed permeability, a high retention capacity and/or a high absorbency under load value.